"The fight against heat is an energy, urban planning and ecological challenge"

Today, it is official: Switzerland is warming up! It is even doing so faster than the global average. At the end of 2025, MétéoSuisse and the Swiss Federal Institute of Technology in Zurich (ETH Zurich) indicated that warming relative to the pre-industrial era already reaches 2.9 °C in Switzerland, compared with 1.3 °C globally. For the existing building stock, the consequences could be considerable, with part of the housing stock potentially becoming uninhabitable in summer without protective measures against heat.

In the face of this development, the fight against heat logically becomes a major concern. We continue our series devoted to this topic by addressing more political aspects with Mohamed Meghari, head of the Energy Efficiency Division at the Directorate of Energy of the Canton of Vaud.

Has the issue of warming urban centers been underestimated by the authorities for too long?

Let us clarify to begin with that the fight against the warming of urban centers cannot be limited to buildings, because it also depends to a large extent on the configuration of cities and land use planning.

This problem has not been underestimated. However, we have not shown much anticipation. The building sector is set within very long time horizons: constructions carried out today are designed to last several decades, often 50 years or more. Renovations also aim for long-term durability. Yet these decisions were made in a climatic context that is no longer that of today and which, moreover, is evolving faster than expected.

In this context, a large part of the current building stock was not designed to cope with current climatic conditions. We are therefore faced with a significant inertia effect, which places us in a situation where it is necessary to adapt an existing stock that was not conceived with these issues in mind.

The current frameworks, notably the Model of Cantonal Energy Regulations (MoPEC) and standards such as SIA 180, now incorporate these issues. However, they apply mainly to new constructions. The main challenge therefore lies in adapting the existing stock, which constitutes — and will for a long time still constitute — the bulk of the built fabric.

Cities are now turning into real ovens during the summer... What can a canton like Vaud do?

It can act at several levels, notably through the Vaud Energy Act (LVLEne), in its revised version adopted by the Grand Council last February, but also via its planning instruments. This includes promoting the greening of urban spaces, reducing soil sealing, and integrating climate issues into urban projects.

In this context, the LVLEne constitutes a relevant lever to act at the source, that is to say from the design stage of buildings and renovation projects. It makes it possible to establish the legislative framework necessary for preventing summer overheating, notably by ensuring compliance with the technical standards in this area, including the SIA 180 standard.

This approach reflects an important shift: the fight against heat islands is now a cross-cutting issue, both energy-related, urban planning-related and environmental.

The current logic is no longer to ban cooling, but to strictly regulate energy needs through building design that limits the risks of overheating.

Shouldn't new incentives or penalty-type mechanisms be introduced?

The current instruments were designed primarily to reduce heating needs. It now appears necessary to rebalance these instruments in order to act on summer overheating in buildings, notably by strengthening incentives to implement passive solutions, such as solar shading or natural ventilation.

The introduction of binding mechanisms must, however, be considered with caution, in order to ensure acceptability and not to hinder investments in energy renovation.

For new constructions, is this issue of fighting heat taken into account when issuing building permits?

The consideration of summer heat has evolved significantly in recent years. Today, this issue is integrated into the authorization procedures framework, notably through the energy requirements applicable to new constructions.

Before the 2014 revision of the Vaud Energy Act (LVLEne), the use of cooling was, in principle, prohibited and only authorized for applications requiring specific climatic conditions, based on proof of need. This approach was in line with the logic of limiting emissions at source, enshrined by the Environmental Protection Act (LPE).

Since that revision, comfort cooling has been allowed, but under strict conditions. Cooling installations must meet high energy performance standards and be accompanied by the compensation of a significant share of electrical needs — generally around 50% — by on-site renewable energy production, notably photovoltaic.

Moreover, the prevention of summer overheating does not rely solely on the question of cooling. The Vaud legal framework acts upstream, at the design stage of projects. The LVLEne and its implementing ordinance require demonstrating, as part of the permit application, compliance with the energy requirements, notably through cantonal forms.

These requirements refer to technical standards, in particular SIA 180, which applies generally, but is not systematically subject to a formal check at this stage. However, when a project includes a cooling system, its conformity is examined more thoroughly to ensure that cooling needs are limited at source and result from an appropriate building design.

As cantonal law evolves, this approach is expected to be strengthened. The new energy legislation indeed provides that compliance with the requirements arising from technical standards, notably SIA 180 and SIA 380/1 — for which systematic checks are already in place — be verified at the building permit stage, both for new constructions and for renovations. This will allow the prevention of summer overheating to be integrated more directly into projects.

In conclusion, the current logic is no longer to ban cooling, but to strictly regulate energy needs while acting at the source, through building design that limits the risks of overheating.

Managing heat is generally more complex, because it depends on a set of interdependent factors.

Between so-called "active" or "passive" cooling, what concrete solutions exist to reduce the effects of urban center warming on the built environment?

Passive solutions are clearly favored today, as they help limit energy needs. They include, in particular, external solar shading, night ventilation, thermal mass, and greening. These approaches are encouraged by current regulatory frameworks.

Active solutions, such as reversible heat pumps, geocooling or cold networks, can complement these measures. However, the use of these systems must remain controlled in order to limit energetic and environmental impacts.

Is it ultimately more difficult to reduce nuisances related to heatwave periods than those associated with severe cold?

Managing heat is generally more complex, because it depends on a set of interdependent factors. Unlike cold, which can be treated effectively with well-mastered technical solutions such as insulation and heating, heat is strongly influenced by the urban context, building design and occupant behavior.

Furthermore, some technical responses, such as air conditioning, can have counterproductive effects by increasing energy consumption or contributing to heat islands. That is why current frameworks, notably MoPEC, the Vaud Energy Act (LVLEne) and SIA standards, are evolving toward a more integrated approach, aiming to act at the source and at the territorial scale.

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